dsa: mv88e6xxx: Centralise common statistics check

With moving information about available statistics into the info
structure, the test becomes identical. Consolidate them into a single
test.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241207-v6-13-rc1-net-next-mv88e6xxx-stats-refactor-v1-2-b9960f839846@lunn.ch


Signed-off-by: Jakub Kicinski <kuba@kernel.org>